Re: BLT StripChart + scrollbar

DESheffer@xxxxxxxxx wrote:
I am currently reading real time data into a BLT StripChart that has
both the -autorange and -shiftby options. As is desired, all older
data is automatically moved to the left, out of view. However, I would
also like to scroll backwards in time (x-axis) to view the older data,
with the option to later return to the -shiftby view. Has anyone done
this sort of thing with a StripChart and scrollbar and care to share
some examples?

I've done it. I can't share any working examples right now because it's all buried in lots of proprietary code, but I can give some advice.

With my current setup, it seems that once I use the scrollbar, the -
shiftby option becomes disabled and cannot be re-set. Is there any way
to get this option back so I can toggle back to the original shifted
mode?

The way I solved this is with a hack in the code that handles scrollbar requests. What I have is something like this:

scrollbar $graph_h_scrollbar ... -command scrollTheGraph
....
proc scrollTheGraph {args} {
global graph

set result [eval $graph axis view x $args]
update idletasks
set viewx [lindex [$graph axis view x] end]
if {$viewx > .999} {
$graph_w axis configure x -min {} -max {}
}
return $result}
}

I don't know recall why I chose .999 (and is proof why Magic Numbers aren't a good idea...). The idea is, if the scrollbar is sufficiently to the right, reset the min and max to null which is what is necessary to re-enable the autoscrolling.

(yuck! revisiting that code now after so many months, I'm chagrined by my use of a magic number and a call to update, but I'm hoping I had a good reason at the time!)

We also have a scale widget that lets you adjust the scale of the graph, and it has the following comment at the top:

"If min and max are configured the autorange has no effect. So, when the scale changes we need to re-enable auto scaling by adjusting the max while keeping the min static"

I hope this helps. It _is_ possible to have autoscrolling and use scrollbars, it just takes some creative coding. The BLT graph widget is amazing, but the docs do leave a little bit to be desired. With enough digging though, just about anything you want to do seems to be possible.


--
Bryan Oakley
http://www.tclscripting.com
.

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